This application is a division of copending application Ser. No. 09/582,140 filed Jun. 19, 2000 now U.S. Pat. No. 6,475,384 as a national stage of PCT/DE98/03733 filed Dec. 16, 1998 and based on German application 197 56 962.5 of Dec. 20, 1997 under the International Convention.
1. Field of Invention
The present invention relates to a method of flotation.
2. Background of the Invention
According to the state of the art, various flotation processes are known. Thus in the publication xe2x80x9cUmweltschutz Entsorgungstechnikxe2x80x9d of Prof. Dr. P. Kunz 2. Auflage 1990 Vogel Book Publishing Co. under the heading xe2x80x9cTreatment of Waste Waterxe2x80x9d on pages 85-86, the electroflotation and pressure-expansion flotation are disclosed.
These processes are also known from the work Wassertechnologiexe2x80x94Fxc3xa4llung, Flockung, Separation of Hermann H. Hahn of Springer-Verlag Berlin, Heidelberg 1987.
In the pressure-expansion flotation, water under pressure is charged with gas and conducted into a flotation chamber. Upon pressure relief, there is an expansion of the gas in the liquid, the gas bubbles out and flotates the solids to be separated from the liquid which can be recovered from the surface of the liquid.
In electroflotation, a gas rising in the liquid is generated by electrolysis and flotates the solids to be separated.
Both processes are used in an industrial scale, but have significant drawbacks. Thus the expansion flotation requires expensive apparatus features in addition to pressurizable apparatus.
As a result of the rapid pressure expansion, the gas formation is rapid, as a result of which turbulence arises which can again break up the flocculate.
In both processes, the flocculating step must precede the flotation step in which the solids precipitate out in a flocculation basin and which agglomerate to larger flocculates.
Electroflotation gives rise to high operating costs because of the high current requirements. Both processes have a high energy consumption.
It is therefore the object of the invention to provide a flotation method which is characterized by a substantially-reduced energy consumption and can avoid the need for expensive and dear apparatus and in which a breakup of the flocculate by turbulence is suppressed.
The object is achieved with the flotation reactor with a flotation space, an inlet for the flotation liquid and a gas source, characterized in that the gas source is a catalyst which is brought into contact with a substance which is converted to a gas thereby.
With the method and the apparatus according to the invention it is possible directly to carry out flotation of solids in an energy-conserving manner at low apparatus cost. The danger that flocculates will be destroyed by the flotation is very low. The flotation is effected with very small gas bubbles and is highly uniform and of low turbulence.
The flotation reactor can have its flotation space coated with the catalyst. The catalyst can have at least one of its components selected from the group of manganese dioxide and active carbon. The flotation reactor can have means at its bottom region for introducing a substance which is converted on the catalyst to the gas. The flotation reactor can also have in the bottom region means for introducing the flotation liquid.
The means for introducing the water for flotation can be a downwardly-directed pipe which at its lower end or in its lower third, has outlet openings and which widens upwardly in the form of a funnel. At the funnel, means can be provided for tangentially admitting the flotating liquid. The flotation reactor can have a downwardly-directed tube and a funnel-shaped converging narrowing. The pipe beneath the outlet openings can have a bottom. The funnel-shaped narrowing can be so configured that it extends above the pipe cross section so that no rising floc or gas bubbles can enter the outlet opening.
The walls of the flotation space can widen upwardly in the form of a funnel.
The aforementioned flotation chamber can be located in a further surrounding flotation chamber and the walls of the flotation chamber can be coated with a catalyst which catalyzes a chemical reaction from which a gas is produced.
In this embodiment the flotation space in its lower region has means for introducing a substance which forms a gas by the chemical reaction. The flotation space can be so constructed that it surrounds the first-mentioned flotation space with its wall radially symmetrically whereby it forms below the means for introducing a substance producing a gas by the chemical reaction, a closed vessel which runs to a central incline and whereby the wall of the flotation space leaves free an intermediate space with the wall of the flotation reactor outside the funnel means can be provided for concentration of gas bubbles in the flotation space. This means for concentrating the gas bubbles can be a conical ring.
The second flotation space can be provided at its bottom in the form of an incline for the discharge of the flotated liquid which can be effected through a U-shaped pipe. The U-shaped pipe can be telescopingly elongatable.
The flotation reactor can have means for separating the flotate.
The flotation method is characterized in that a chemical reaction is carried out for producing gas bubbles. The chemical reaction can be a catalytic reaction, for example, a decomposition of hydrogen peroxide to water and oxygen. As the catalyst, manganese dioxide and/or active carbon can be used.
The substance which decomposes to the gas in the chemical reaction can be admitted to the lower region of a flotation space. The substance to be flotated can be supplied in a tangential flow and can then flow in a downwardly-directed stream.
The liquid quantity leaving the flotation reaction is preferably matched to the flotation liquid at the inlet to the flotation reactor.